1. Field of the Invention
The present invention relates to a zoom lens having a function which changes an angle of view by changing a focal distance, and a zoom lens suitable for an imaging device which obtains subject image data by using an imaging element. In particular, the present invention relates to a compact zoom lens suitable for a digital camera which images a still image, a video camera which images a moving image or the like, an imaging device and a portable digital device using such a zoom lens as an imaging optical system.
2. Description of the Related Art
In recent years, widespread digital cameras are requested to be further downsized and to offer additional technical advantages. Such digital cameras include an autofocus (autofocus adjustment: hereinafter referred to as AF) function, and the digital cameras including such an AF function are requested to have an increased autofocus speed (hereinafter referred to as AF speed). Zoom lenses often adapted to many digital cameras as a shooting lens are also requested to be downsized and offer additional technical advantages.
In order to downsize the zoom lens, it is necessary to reduce the entire length of the zoom lens (distance from most object side lens surface to image side) when used. It is also necessary to downsize a focusing lens in order to increase an AF speed.
Moreover, it is necessary for the zoom lens to have resolution corresponding to an imaging element having at least 10 million pixels over the entire zoom area in view of the application to a high-end digital camera in order to offer additional technical advantages.
A zoom lens including, in order from an object side, a first lens group having a positive focal length, a second lens group having a negative focal length, a third lens group having a negative focal length, a fourth lens group having a positive focal length, and a fifth lens group having a positive focal length is widely known as a zoom lens suitable for a high zoom ratio. Examples of such a zoom lens including a five-lens group configuration of positive, negative, negative, positive and positive are disclosed in Patent Document 1 (JP3716418B) and Patent Document 2 (JP4401451B), for example.
Patent Document 1 discloses as a specific example a zoom lens having a five-lens group configuration of positive, negative, negative, positive and positive, and performing focusing by moving the third lens group as a focus group. In such a zoom lens, the third lens group is a cemented lens made of two lenses of negative and positive, so the third lens group is likely to be increased in size and weight. Therefore, a load for moving the focus group is increased, so that a motor which drives the focus group is increased in size, and thus, a long time is required for the focusing operation.
Patent Document 2 also discloses as a specific example (for example, Embodiment 4) a zoom lens having a five-lens group configuration of positive, negative, negative, positive and positive, and performing focusing by moving the third lens group as a focus group. In such a zoom lens, the third lens group has three lenses of negative, positive and negative, so the third lens group is likely to be increased in size and weight. Therefore, a load for moving the focus group is increased similar to the case in Patent Document 1, so that a motor which drives the focus group is increased in size, and thus, a long time is also required for the focusing operation.
Namely, although the configurations disclosed in both of Patent Documents 1, 2 are suitable for a high zoom ratio, and are expected to be downsized, to increase an AF speed and to offer additional technical advantages, the focus group is increased in size and weight. For this reason, a load for moving the focus group is increased, so that a motor which drives the focus group is increased in size, and thus, a long time is required for the focusing operation.